1. Field of the Invention
The present invention relates to a projector, and more particularly, to a projector that can adjust relative positions of an image modulator and a lens.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective view of a projector 10 according to the prior art. The projector 10 comprises a supporting frame 12, a lens 14, a digital micromirror device (DMD) 16, a frame 18, and a circuit board 20. The lens 14 and the DMD 16 are installed on two sides of the supporting frame 12 respectively. The supporting frame 12 fixes the relative position of the lens 14 and the DMD 16. The frame 18 fixes the DMD 16 to the supporting frame 12. The circuit board 20 electrically connects and transmits data to the DMD 16. Many problems may affect the imaging quality of the projector 10. For example, slight inaccuracies in component surfacing or placement may result in a blurred or distorted image. From optical principles, a fine focus requires relative positions of the DMD 16 and the lens to be parallel. With the positions of the DMD 16 and the lens 14 being determined, the supporting frame 12 for installing the DMD 16 and the lens 14 determines the resulting imaging quality. In other words, the two sides of the supporting frame 12 must be as parallel as possible. This is difficult to achieve in mass production. The error in placement can be limited to an acceptable range, however, this affects the imaging quality.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of an imaging principle. In general, the imaging principle includes transmitting light of an object 22 through a lens 24, and focusing au image 26 on a screen. The light beam parallel to the line L of the lens 24 is refracted across the focal point F of the lens 24. The light passing through the center O of the lens 24 goes straight. An intersection point of the two light beams is the position of the image 26. A point A of the object 22 focuses on a point a of the screen. When the object 22 and the lens 24 are parallel, every point of the object 22 will focus on the screen to clearly form the image 26. When the object 22 and the lens 24 are not parallel, the light beam parallel to the line L of the lens 24 is refracted across the focus F of the lens 24, and light passing through the center 0 of the lens 24 travels straight, and a point B of the object 22 will focus on a point b off the screen.
From the above description, to achieve a clear image on the screen, the object 22 and the lens 24 must be parallel. For the projector 10 to have high imaging quality, the DMD 16 and the lens 14 have to be installed on two parallel surfaces respectively. The projector 10 according to the prior art uses the supporting frame 12 to fix the DMD 16 and the lens 14 and controls the out-of-parallel of the two sides of the supporting frame 12 in an acceptable range with mechanical design. The rigidity of the supporting frame 12 is also strengthened to prevent deformation caused by improper force during installation of the DMD 16 and the lens 14. However, the DMD 16 and the lens 14 have imprecise dimensions themselves, and with an error in placement through the supporting frame 12, the total error from parallel placement is often unacceptable. Therefore, the projector cannot project a clear image on the screen. Some projector manufacturers require lens manufacturers to provide lenses with less sensitivity to placement. Some projector manufacturers use spacers installed between the lens and the supporting frame. However, such spacers have fixed size so perfect focus is never achieved. In addition, other projector manufacturers match the lens with the supporting frame, matching defects in hope that they cancel out. Such matching is difficult and makes maintenance and part replacement inconvenient.
It is therefore a primary objective of the claimed invention to provide a projector and a method of adjusting the relative positions of the image modulator and the lens to solve the above-mentioned problem.
According to the claimed invention, a projector and a method for assembling a projector are provided. The projector comprises a lens; a supporting frame including a first fixed side, a second fixed side, and a elastic protrusion, the first fixed side having a first screw hole, the second fixed side having a second screw hole; a fixing device having a first through hole and a second through hole respectively located corresponding to the first screw hole and the second screw hole; and an image modulator installed between the supporting frame and the fixing device, the image modulator having a first modulator side corresponding to the first fixed side of the supporting frame, and a second modulator side corresponding to the elastic protrusion.
The claimed method comprises (a) tightly screwing the first screw into the first screw hole through the first through hole to combine the fixing device and the supporting frame, the first modulator side of the image modulator fixed on the first fixed side of the supporting frame; (b) loosely screwing the second screw into the second screw hole through the second through hole making the second modulator side of the image modulator contact the elastic protrusion; (c) projecting an image to a screen, adjusting the lens to focus the image from the first modulator side of the image modulator on the screen; and (d) adjusting the second screw in the second screw hole making the image modulator press the elastic protrusion to move until the image from the second modulator side of the image modulator is in focus on the screen.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.